Cisco Systems 78-11741-02 Requesting Source Information from an Msdp Peer, Redistributing Sources

Configuring Multicast Source Discovery Protocol

MSDP Configuration Task List

Requesting Source Information from an MSDP Peer

Local RPs can send SA requests and get immediate response for all active sources for a given group. By default, the router does not send any SA request messages to its MSDP peers when a new member joins a group and wants to receive multicast traffic. The new member just waits to receive the next periodic SA message.

If you want a new member of a group to learn the current, active multicast sources in a connected PIM-SM domain that are sending to a group, configure the router to send SA request messages to the specified MSDP peer when a new member joins a group. Doing so reduces join latency, but requires some memory.

Note that information can be requested only from caching peers.

To configure this feature, use the following command in global configuration mode:

Command	Purpose
Router(config)# ip msdp sa-request	Configures the router to send SA request messages to the specified
{peer-address peer-name}	MSDP peer when a receiver becomes active, so the receiver can
	learn about multicast sources in a group. The peer replies with the
	information it is SA cache. If the peer does not have a cache
	configured, this command provides nothing.

Repeat the preceding command for each MSDP peer that you want to supply you with SA messages.

An alternative to requesting source information is to cache the SA state, which is described in the section “Caching SA State” earlier in this chapter. If you cache the information, you need not trigger a request for it.

Controlling Source Information That Your Router Originates

There are two ways to control the multicast source information that originates with your router. You can control the following:

•Which sources you will advertise (based on your sources)

•Whom you will provide source information to (based on knowing who is asking you for information)

To control which sources you will advertise, see the following section, “Redistributing Sources.” To control whom you will provide source information to, see the section “Controlling Source Information That Your Router Forwards” later in this chapter.

Redistributing Sources

SA messages are originated on RPs to which sources have registered. By default, any source that registers with an RP will be advertised. The “A flag” is set in the RP when a source is registered. This flag indicates that the source will be advertised in an SA unless it is filtered with the following command.

Cisco IOS IP Configuration Guide

IPC-481